STKS: buy at the bid, sell at the offer

[Dick Crotinger <richinger@xxxxxxxxxxxxxxxx>]

I've often heard that floor traders in the equity and options markets
have a great number of advantages over the rest of us, particularly with
respect to commissions, speed, and especially being able to "buy at the
bid and sell at the offer."  How do they do this?  I can see being able
to "offer at the offer price" or "bid at the bid price," and wait until
someone takes the other side of the trade.  But I've often noticed, when
a stock starts to move, that a 10-lot (or 100-lot) of one of her juicier
options gets bought (at the bid) or sold (at the ask), in either case
the opposite of what I would do if I were about to enter a trade there. 
I'm assuming that a floor trader or market maker "plucks the apple" just
before it starts to move... often, the bid/ask changes immediately
thereafter (and typically such that the trade just consumated becomes
immediately profitable).

	I'm not assuming that us mortals should or could accomplish the
above... merely wondering how it's done.  Any and all explanations
appreciated.

Dick Crotinger
richinger@xxxxxxxxxxxxxxxx